Regardless of the exact mechanisms by which temporal summation of allodynia is generated, the phenomenon is likely to be at least part of the basis for CRPS patients' ongoing ''spontaneous'' pain. It has been suggested that temporal summation of A-beta allodynia provides at least part of the basis for ongoing background pain in neuropathic pain patients (17). This relationship could occur if continuous input from A-beta low threshold afferents (evoked in the normal course of mechanical stimulation from walking, sitting, or even contact with clothes) activated slow temporal summation of a type of burning, aching, or throbbing pain that built up slowly and dissipated slowly over time. This possibility was explicitly tested in a group of 31 CRPS patients by comparing intensities of ongoing pain between 10 patients who demonstrated slow temporal summation with 17 who did not (17). The former had significantly higher intensities of ongoing pain (mean = 7.02 on visual analog pain scale) than the latter (mean = 4.04 on visual analog pain scale; p < .001). Therefore, exaggerated or abnormally triggered mechanisms of slow temporal summation are likely to form at least part of the basis of persistent pain that usually occurs in CRPS patients.
TESTING VISCERAL AND CUTANEOUS HYPERALGESIA IN IRRITABLE BOWEL SYNDROME PATIENTS Visceral Hyperalgesia in Irritable Bowel Syndrome Patients Evidence for Visceral Hyperalgesia in Irritable Bowel Syndrome
Tests similar to those described above for CRPS and fibromyalgia patients also have been used to characterize pain in IBS. IBS is one of the most common disorders seen by gastroenterolo-gists. Patients classically present with chronic abdominal pain associated with an alteration in bowel habits. It is now well accepted that the majority of patients with IBS demonstrate enhanced perception of balloon distension of the rectum (Fig. 3, left panel). This visceral hypersensitivity is manifested by increased intensity of sensations, lowered thresholds for visceral pain, and/or exaggerated viscerosomatic referral in comparison to control subjects (40-42). Visceral hypersensitivity is a biological marker of IBS (41).
Was this article helpful?